In a double boiler, whisk Polenta into boiling water, stirring often to prevent lumping. Cover and steam for 30 minutes on low heat, until cornmeal is softened. Stir in corn, rosemary and cheese. Spread mixture into an 20 cm greased springform pan, pressing the mixture with a spoon to move the mixture up the sides of the pan forming an empty shell. Allow the shell to cool and harden. Grill all vegetables. Season with salt and pepper. Layer the vegetables and chopped basil in pie shell in a decorative pattern. Chill and unmold . Serve at room temperature.